Reduced excess viscosity

The intrinsic viscosity refers to the limit of a zero polymer concentration and thus deals with the effect of completely separated chains on the solution viscosity only. For finite concentrations the chains partially overlap, which leads to an increase of the reduced excess viscosity. The increase is well-described by... 

The Coulomb forces with the resulting build-up of structures in polyelectrolyte solutions also have drastic consequences for the solution viscosity. Variations in the viscosity with the polymer content are conveniently discussed in terms of the reduced excess viscosity (Eq. (8.161)). For solutions of neutral polymers increases slowly with the polymer concentration Cw, as described by Eq. (8.169). Polyelectrol3de solutions exhibit a quite different behavior. They show very high values of 7r already at very low polymer concentrations and one then often observes a drop rather than an increase with c. Curve 1 in Fig. 8.19 gives a typical example of this behavior. The decrease can be empirically described by the Puoss-Strauss relation... 

Fig. 8.20. Concentration dependence of the reduced excess viscosity measured for aqueous solutions of NaPSS for left) various molar masses at a constant salt concentration Cg = 4 xl0 molP and (right) for a sample with a molar mass Mw = 1.6 xlO g moP for different concentrations of NaCl. Prom Cohen et al. [108]...

Dynamite nitrocotton is pulped within as short a period of time as possible, e.g. 2 hr, because excessive beating of the product reduces the viscosity of the nitrocellulose solutions. The pulping is followed by washing or by a short poaching in boilers, after which the purity is checked by means of the heat test. After stabilization, the nitrocotton is freed from sand and. other impurities. 

Excessive load, reduced fluid viscosity, and low speed can cause a breakdown of the lubrication layer to the point of a metal-metal contact. Direct adhesive contact can lead to molecular interaction strong enough to tear material out of the surface. This process is also known as cold welding . Metal surfaces under ambient conditions are usually covered with oxide layers that prevent cold welding at moderate loads. 

Solvents that meet all or most of the criteria are propylene carbonate, dimethyl sulfoxide, 4-butyrolactone, acetonitrile, sulfur dioxide, thionyl chloride, and phosphorus oxychloride. Certain other solvents, with fairly low s values, such as tetrahydrofuran, dimethoxyethane, and 1,3-oxolane are used in conjunction with a high s solvent, in order to reduce the viscosity without impairing excessively the other desirable properties of the co-solvent. All these solvents are on the List, with properties shown in the tables mentioned. Commercial implementation of such batteries has been highly successful, with energy densities of primary dischargeable batteries of 0.3 W h g 1 or 0.5 W h cm 3 and a self discharge rate of < 2% per year of the open-circuit battery being achieved. 

Monomers are usually low-MW, monofunctional materials that chemically incorporate into the cured coating rather than volatilize into the atmosphere, as is common with solvent diluents. Monomer diluents are chosen on the basis of providing good solvency, effectively reducing the viscosity of the oligomer without excessively retarding the cure rate. Certain diluents will contribute to the physical properties of the adhesive. However, generally they provide soft, thermoplastic films because of their linear and uncrosslinked nature. 

The lower degree of polymerization of hyaluronic acid present in rheumatoid fluids (B3, BIO, B13, B18) undoubtedly impairs the effectiveness of the fluid as a lubricant between joints. Another factor contributing to this may be the lower concentration of hyaluronic acid found in certain rheumatoid effusions. Special viscosity and elastic properties are exhibited by hyaluronic acid in synovial fluid in concentrations in excess of 0.2 g/lOO ml (Bll) the concentration of hyaluronic acid in inflamed joint fluids of rheumatoid arthritis is generally less than this value. In a recent investigation, Hamerman and Sandson (H4) found that, apart from a reduced anomalous viscosity, the hyaluronate-protein complexes of synovial fluid differed from normal and showed increases in both protein content and amounts of basic amino acids. 

The prolonged retention of viscous airway secretions in the diseased lung (e.g., CF and COPD) can lead to recurring bacterial infections, resulting in a viscous, more purulent sputum [155]. Increased mucus viscoelasticity may be attributed to extensive disulphide and lectin bonding, poor hydration, and/or excess concentrations of extracellular DNA or actin [155], In these situations, therapeutics have been used to reduce the viscosity of airway secretions to improve the rate of mucociliary clearance. 

Chemicals that reduce the bulk viscosity and increase drainage can cause a decrease in foam stability. The same applies to materials that reduce surface viscosity and elasticity (swamping the surface layer with excess compound of lower viscosity). 

USE Natural colloid, gelling agent, viscosity control agent used primarily in food products but also in pharmaceuticals. Also in products for diabetics, proprietaries for reducing excess body wt, toothpastes. As carrier for food preservatives, bactericides. In bacteriological culture media. 

Unsaturated polyester resins are mainly made by condensing a dibasic acid (1,2-propanediol) with an anhydride (maleic or phthalic anhydrides), by forming ester linkages between the dibasic acid (or their anhydrides) and glycols. Then a reactive monomer (mostly styrene or vinyl toluene, MMA or diallyl phthalate) is used to crosslink the system when needed. Unsaturated denotes the uncompleted chemical activity (double bond) in the original structure, which are used for crosslinking afterwards. In this context, an excess of styrene as the crosslinker (10 to 50 %) is usually added to have it ready in the system, as well as to reduce the viscosity. There are also certain accelerators used (such as, cobalt naphthenate or tertiary amines like dimethyl aniline) to facilitate the cure at ambient temperatures. In addition, there may be pigments, fillers, various inhibitors, accelerators, stabilisers and flame retardants, added to the system. Polymerisation is activated whenever a catalyst (i.e., benzoyl or methyl-ethyl-ketone peroxide) is added. 

The prepolymer can be synthesized by a simple one-pot synthesis . During a first step an NCO-terminated prepolymer is prepared by a reaction of the polyol with an excess of TDI. The second step comprises the reaction of all remaining NCO groups with the silane 1. Phenyltrimethoxysilane 2 serves to reduce the viscosity of the prepolymer mixture. It has already been added during the prepolymer synthesis. 

Oil displacement experiments were performed under different salinity conditions (1) constant salinity of pol3nner solution at 1.5% NaCl (i.e. optimal salinity of the soluble oil formulation), and variable connate water salinity (2) constant salinity of connate water at 1.5% NaCl and variable salinity of pol3mier solution and (3) the salinity of polymer solution equals the salinity of connate water, both varied simultaneously. Sand packs were chosen as the model porous media in order to avoid the effects of porous media heterogeneity, clays and surfactant adsorption loss. The compositions of aqueous formulation and soluble oils are specified in Figures 1 and 2. The difference between their compositions reflects the density difference between water and dodecane whereas the surfactant and alcohol concentrations (w/v) are the same in both types of formulations. The polymer solution used was 1000 ppm PUSHER-700 in brine. For polymer solution in distilled water, the polymer concentration was reduced to 250 ppm to avoid excessive viscosity. Several experiments were repeated and the reproducibility was established to be within 2% in tertiary oil recovery. 

Care must be taken to control the cross-link density (the amount of cross-links per polymer chain) of a polymer for one critical reason excessive cross-linking can prevent polymers from fully extending in solution. This manifests itself in a reduced solution viscosity, as schematically suggested in Figure 19. Normally water-soluble polymers can even be made insoluble when the cross-linked density is sufficiently high to prevent uncoiling and solvent intrusion. 

---